1. Field of the Invention
The present invention relates to a picture processing apparatus, a picture processing method, and a program for processing a digital picture.
2. Description of the Related Art
The recent years have witnessed widespread acceptance of picture processing apparatuses that handle picture information in digitized form for highly efficient transmission and storage of the picture information by taking advantage of redundancies specific to this type of information. Particularly in widespread use is the kind of apparatus that conforms to the MPEG (Moving Picture Experts Group) standard or the like involving data compression through orthogonal transformation such as DCT (Discrete Cosine Transform) and motion compensation.
Predicting motion compensation is thus one of the important elements of moving picture compression encoding and decoding technology. Motion-compensating prediction is a technique for detecting how a series of pictures making up a moving picture has moved and utilizing pixel information derived from the detection as predicted pictures for efficient compression.
According to typical moving picture compression techniques such as the MPEG, motion-compensating prediction is effected by comparing each of divisions called macro blocks (MB) making up each picture with the pixel information of the preceding or subsequent picture in order of display. Such moving picture compression techniques involve the use of a motion vector indicative of the direction and magnitude of a motion. The picture to be compared with is called the reference picture or reference plane hereunder.
MPEG-4 AVC (Advanced Video Coding) established recently as a new moving picture compression encoding and decoding standard introduces novel techniques intended to enhance the efficiency of encoding in motion-compensating prediction.
One of these techniques for AVC allows a different reference plane and a different motion vector to be designated for each macro block or for each of two or four divisions making up the whole macro block, as shown in FIGS. 1A through 1D.
Where a given macro block is divided into four divisions, each of the divisions is called a sub-macro block. As indicated in FIGS. 2A through 2D, a different motion vector can be further designated for each sub-macro block or for each of two or four divisions constituting the whole sub-macro block.
The dividing of the macro block is also available for bidirectional motion-compensating prediction, so that a different motion vector can be designated for each of up to eight different reference pictures and for up to 32 divisions making up each macro block. In practice, however, there are level constraints on the number of motion vectors regarding two adjacent macro blocks.
Another technique for motion-compensating prediction under the MPEG-4 AVC involves the use of a six-tap interpolation filter with regard to brightness information. For this reason, as shown in FIGS. 3A through 3C, the processing of the interpolation filter requires transferring from an external memory five pixels of pixel information for each of both the vertically and the horizontally enlarged areas encompassing each of the divisions constituting macro block.